diff --git a/REQUIRE b/REQUIRE
index 1089557c..405e23cc 100644
--- a/REQUIRE
+++ b/REQUIRE
@@ -1,3 +1,3 @@
 julia 0.6
 BenchmarkTools 0.2.1
-Compat 0.37.0
+Compat 0.44.0
diff --git a/src/problem/SparseFEM.jl b/src/problem/SparseFEM.jl
index a9bb6a4f..1de14ea4 100644
--- a/src/problem/SparseFEM.jl
+++ b/src/problem/SparseFEM.jl
@@ -20,7 +20,7 @@ end
 
 # timing of assembly, slice and solve
 function perf_sparse_fem(N)
-    Ifree = get_free(N)
+    Ifree = [LinearIndices((N, N))[i] for i in get_free(N)]
     # assembly
     A = fdlaplacian(N)
     # boundary condition